1. Field of Invention
The invention relates to masking stitch errors between swaths during printing.
2. Description of Related Art
Fluid ejecting devices such as, for example, inkjet printers, fire drops of fluid from rows of nozzles of an ejection head. The nozzles are usually fired sequentially in groups beginning at one end of the head and continuing to the other end of the head. While the nozzles are being fired, the head moves at a rate designed to advance it by a resolution distance before the next firing sequence begins. If the nozzles are not fired simultaneously, the rows of nozzles can be tilted so that drops fired from all nozzles land in a substantially vertical column.
The ejection head can have one or more dies, each die having a plurality of nozzles. Some devices have ejection heads with only one die, and some devices have ejection heads with multiple dies. If an ejection head has multiple dies, the dies can be, for example, arranged vertically with respect to one another so that the head can eject more drops in a single swath of the head compared to a head having a single die.
The line at which the swaths ejected by adjacent dies meet, or at which the adjacent swaths meet, is called the stitch joint. Stitch joint errors occur when the swaths meeting at the stitch joint meet in such a way that the resulting arrangement of drops at one side of the stitch joint of a printed image are displaced from the drops on the other side of the stitch joint by a different distance than the displacement distance between drops within a swath. This creates a visible, undesirable print defect. Because of the spacing of the stitch joint errors, the stitch joint errors are very noticeable because the human eye is very sensitive to this spatial frequency region.
Stitch joint error can be, for example, the result of a gap between the drop of one die or swath adjacent the stitch joint and the drop of an adjoining swath or die adjacent the stitch joint. The gap is usually caused by difficulties in producing adjacent swaths close enough together to mask this apparent error.
It is desirable to cover up or mask the stitch joint error. Prior art techniques for masking the stitch error between swaths require alternating the firing of the nozzles of adjacent dies in a multi-die ejection head using different firing sequences. However, it is often difficult to precisely position adjacent dies so that the spacing between the lowermost nozzle of the upper swath and the uppermost nozzle of the lower swath is reduced enough so that the stitch joint error becomes less apparent.
This invention provides systems and methods for indexing the position of a sheet of recording medium conventionally and then measuring the position of the sheet of recording medium accurately by a sensor.
This invention separately provides systems and methods for shifting the data in the printhead so that the data is accurately aligned within a predetermined pixel accuracy to the known paper position.
This invention separately provides systems and methods for shifting the position of the printhead so that the data is accurately aligned within a predetermined pixel accuracy to the known paper position.
This invention separately provides systems and methods for covering up the resulting stitch joint error by modifying the pixels at the stitch joint interface to mask the apparent error.
In various exemplary embodiments of the systems and methods of this invention, a sheet of recording medium is indexed crudely. The resulting position is measured more accurately using a sensor. The sensor provides this information to a controller. In various exemplary embodiments, the systems and methods of this invention shift the data in the printhead so that the data is aligned within a predetermined pixel accuracy to the measured paper position. In various exemplary embodiments, the remaining sub-pixel stitch joint error is covered up by modifying the pixels at the stitch interface.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.